Dell N3200-ON Networking N-Series Switches User Guide version 6.8.0 - Page 1515

WRED NOTE: WRED is not supported on the Dell Networking N1500 Series switch. WRED Processing Traffic ingressing the switch can be assigned to one of four drop probabilities based on a set of matching criteria. There are three drop probabilities for TCP traffic (green, yellow, and red) and one drop probability for non-TCP traffic (all colors). Users may configure the congestion thresholds at which packets queued for transmission are dropped for each color. WRED is intended to provide early feedback to protocols (e.g., TCP) that depend on packet drop to adjust their transmission rate. WRED packet drops only occur when the system is congested within the ranges specified. If congestion exceeds the upper limit, packets will be dropped at the rate of traffic ingressing the system, e.g., 100%. If the congestion is less than the lower limit, no packets will be dropped. WRED Drop Probabilities Between the minimum and maximum thresholds, the drop probability is divided into eight discrete levels of increasing probability of packet drop. The levels are as follows: 0 - 6.25% of maximum drop probability 1 - 18.75% of maximum drop probability 2 - 30.25% of maximum drop probability 3 - 43.75% of maximum drop probability 4 - 56.25% of maximum drop probability 5 - 68.75% of maximum drop probability 6 - 81.25% of maximum drop probability 7 - 92.75% of maximum drop probability As an example, with a drop probability of 50%, a minimum threshold of 10% and a maximum threshold of 90%, the drop probability from 10% to 20% congestion is 3.125%, from 21% to 30% congestion is 9.375%. Differentiated Services 1515